|Publication number||US5325708 A|
|Application number||US 07/934,176|
|Publication date||Jul 5, 1994|
|Filing date||Aug 21, 1992|
|Priority date||May 14, 1992|
|Publication number||07934176, 934176, US 5325708 A, US 5325708A, US-A-5325708, US5325708 A, US5325708A|
|Inventors||Mauro De Simon|
|Original Assignee||Varian S.P.A.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Referenced by (22), Classifications (7), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Outi =K.(Ia -50.i)
I0 =(Out1 /K+50.i)
The present invention relates to an improved helium detecting unit of the kind employed when searching for leaks in ducts and chambers located in places that are particularly difficult to be accessed and spread over an extended range, far from power supply sources.
For detecting leaks in ducts and chambers of various type and shapes, such as for example the underground pressurized ducts housing telephone cables, there are presently employed techniques using units capable of detecting the concentration of a gas which has been put into the duct the integrity of which has to be tested, and leaks out through cracks that may be present in the duct and can therefore be captured by the detecting unit located outside.
Such units can detect a change in the concentration of a single gas in the gas mixture usually composing the air at ground level, and allow for discovering leaks, if any, due to conduit breaking or cracks with a good accuracy both in respect of the leak location and of the amount thereof.
Units of the above described kind, using helium as a tracing gas, have been disclosed in Italian patents No.s 1 179 600 and 1 224 604 and in EP-A-0352371 in the name of the present Assignee.
The above and other similar devices are equipped with a chamber which is preferably cylindrical, within which a thin quartz capillary is located, being well known that quartz is permeable to helium only when heated to a temperature comprised between 300° and 900° C., wherein one end of the capillary is closed and the opposite end is open and connected to the suction inlet of a UHV (Ultra High Vacuum) pump.
In EP-A-0352371 there is disclosed a helium detector comprising an ion pump and a sniffer probe formed by one or more capillary tubes of silica glass that are closed at one end and connected to the ion pump at the opposite end. A heating filament wound about the capillary tube heats the capillary to a temperature of about 750° C. at which temperature the silica glass becomes permeable substantially to helium only. The ion current drawn by the pump is representative of the helium concentration in the gas mixture to be sampled.
Suitable electronic control systems take care of stopping the heating of the filament when high concentrations of helium are present in order to prevent such gas accumulating within the capillary with a consequent delay of the response to changes of helium concentration in the gas mixture to be analyzed.
The above described devices show anyhow some significant short comings when the units are to be used for checking the condition of ducts or chambers that are located in positions hard to be accessed, such as when they are buried under roadbeds and in sections that are quite long.
In the first mentioned case the weight of the conventional units as well as their construction which is not suitable for an efficient working in presence of dust, mould and other external agents, are an obstacle to the good operativeness of the apparatuses, tire the operator and are subject to frequent clogging with a consequent worsening of the performance.
In the second mentioned case since it is necessary to work over long distances and far from mains power supply sources, auxiliary mobile supply units are to be provided for.
A further shortcoming of the above mentioned units resides in that they have been found subject to an internal overheating after an uninterrupted and prolonged use, particularly in the junction zone between the capillary membrane and the flange provided on the suction inlet of the ion pump, this resulting in a detachment of the UHV (Ultra High Vacuum) seal between the capillary and the flange, thus rendering the detecting unit unserviceable.
A further shortcoming is due to the fact that the above described sensing systems exhibit a large inertia of response when passing from a low helium concentration zone to a high helium concentration zone and vice versa, thus rendering the detection slow and unaccurated.
Finally due to the absence of control devices in the above apparatuses, it may happen that apparatuses that are inoperative or not properly working are employed without the operator's knowledge.
The object of the present invention is that of providing an improved unit for detecting helium leaks which is very reliable and accurate, adapted to be used under particularly difficult conditions, that has a good service autonomy and is easy to be handled and used.
An additional object of the present invention is that of providing a unit of the above mentioned type allowing long periods of operativeness between the maintenance and servicing interventions, and is capable of a prolonged and uninterrupted use.
The above as well as additional objects are achieved by imparting to the device of the invention the characteristics recited in the attached claims.
Additional characteristics and advantages of the invention will be better understood from the description of a preferred but not exclusive embodiment of the unit which is illustrated as a non limiting example in the attached drawings.
FIG. 1 is a cross-section partial side view of the unit;
FIG. 2 is a cross-section partial front view of the unit;
FIG. 3 is a side view of the unit;
FIG. 4 is a block diagram of the mechanical and electronic parts forming the unit;
FIG. 5 is a graph illustrating the characteristic quantities versus the helium concentration;
FIG. 6 is a diagram illustrating the flow of the operations for starting the ion pump;
FIG. 7 is a graph illustrating the output signals of the summing modules.
With reference to FIG. 1, the unit of the invention comprises a quartz capillary membrane 2 having a circular cross-section area of about 1 cm2 with a closed end 3 and an open end 4. Around the middle area of this capillary membrane 2 a platinum filament 8 is wound for about 3/4 of the length thereof leaving a free portion 5 towards the closed end 3 and a free portion 6 towards the open end 4, such filament being adapted to heat the capillary membrane 2 by contact when an electric current flows in the filament.
Portion 6 of the capillary membrane 2 partially protrudes through a hole into a flange 7 provided at the suction inlet of an ion pump 1.
An UHV (Ultra High Vacuum) seal 9 is fixed by an epoxy resin between a hole in a connecting flange 7 and the outer surface of the portion 6 of the capillary membrane 2.
Outside the connecting flange 7 there is provided a first cylindrical hollow member 10 formed by a semirigid plastic material with thermal insulating characteristics, within which at one end the connection flange 7 is partially fitted and at the other end a first cylindrical drilled support 11 is fitted which is adapted to retain one end of a quartz cylindrical tube 12. The opposite end of tube 12 is retained in a similar manner within a second cylindrical drilled support 13 which in turn is partially fitted into a second cylindrical drilled member 14 of a plastic material having thermal insulating characteristics.
A sintered filter 15 is housed within said second cylindrical drilled member 14, which is adapted to cool the gas flow passing from the chamber 16 defined by the inside of the cylindrical tube 12 towards the outside.
This way the gas reaches a temperature of about 150° at a distance of 1 cm from the filter 15. The filter 15 further acts as a flame barrier in case the gas to be sampled is inflammable.
The inner surface of the quartz tube 12 is coated by a reflecting film of aluminum or alternatively it is treated with a glass aluminizing process in order to reduce the loss of heat due to radiation from the filament and the capillary membrane.
Elastic rings 26 are further provided ouside the cylindrical member 14 in order to damp the vibrations of the unit in respect of a possible housing (not shown).
In order to protect the cylindrical tube 12 and to create a gap 27 for thermally insulating the chamber 16, there is provided a tubular housing 17 of stainless steel which is fitted at one end to the first cylindrical member 10 and at the other end to the second cylindrical member 14.
The housing 17 is further provided with a side hole 18 passing through the cylindrical member 10 too and drilled in correspondence of the free portion of said cylindrical member 10 which is comprised between the portion fitted with the flange 7 and the portion fitted with the cylindrical support 11, into which hole is press fitted a sleeve 19 connected to a flexible duct 20 from an auxiliary sampling pump 29 for pumping the air sucked from the outer environment and to convey it into the chamber 16 through the duct 20, the sleeve 19 and the hole 18.
The above construction is quite different from that of the prior devices wherein the sampling pump takes the sampled gas from the chamber containing the capillary membrane, with the gas passing then into the high temperature sampling pump.
According to the present invention since the flow of the incoming gas to be sampled is directed towards the glued zone between the membrane 2 and the flange 7, it allows for the cooling of the glued zone and prevents the melting of the UHV seal.
There is provided a set screw 21 passing through both the wall of the housing 17 and the first cylindrical hollow member 10 for pressing against the connection flange 7 in order to maintain in position the flange 7 and allowing for the extraction of the flange 7 for inspecting the capillary membrane 2.
The free ends of the heating filament 8 are connected to the ends of the electric connections 22 and 23 coming from a feeding unit and retained in the first and second drilled support 11 and 13 respectively.
A recess 28 is provided on a side of the above mentioned ion pump 1 and contains a pellet of a Zr/V/Fe alloy, a material adapted for absorbing gases that do not belong to the group of the noble gases, particularly hydrogen, that may be present in the capillary membrane, this device being known in the art as a chemical pump or a "getter".
Such gases other than helium constitute the background noise when the unit evaluates the helium concentration and according to the present embodiment they are removed by a static device such as a chemical pump, so that a high accuracy of the measurement can be achieved while keeping the temperature of the capillary membrane relatively low, typically 550° C., thus allowing for a considerable power saving of the unit.
The edge 24 of such recess 28 is folded and welded during the assembly and is protected by a cap 25 of soft plastics to prevent the operator being hurt during the assembly and the subsequent inspection of the unit.
The ion pump 1 and the sampling pump 29 are mounted on opposite faces of a flat metal member or plate 37 through screws 38 and 39 with elastic members 40 and 41 being interposed therebetween. At the inlet of the sampling pump 29 there is inserted a suction duct 42 having at its free end a filter 43 for stopping impurities.
Moreover the filter 43 acts as a flame barrier like the already discussed filter 15, in case the gas to be sampled is inflammable.
The unit of the present invention further comprises electronic signal processing means that controls the functions or tasks carried out by the above illustrated components and supplies information about the working condition of the unit, as well as about the presence of helium in the gas mixture under examination and about the amount of such concentration.
Referring now to FIG. 4, the unit of the present invention comprise a device 30 for feeding a high voltage to the ion pump 1, with a current measuring stage 32 for measuring the current drawn, such measuring stage supplying an output signal Ia to the processing and control module 33.
Such feeding device 30 can supply the ion pump with a voltage that can be switched from a steady state current of 3,000 V and a trigger voltage of 6,000 V.
Still with reference to FIG. 4, for completeness there are schematically shown a sampling pump 29 equipped with an inlet filter 43 and a suction duct 42, a duct 20 connecting the sampling pump 29 with the sampling chamber 16, provided with a gap 27 and a sintered filter 15 housing the capillary membrane 2 about which there is wound the heating filament 8 fed through the connections 22 and 23 of the feeding unit 31.
A stage 34 is further provided for supplying to the processing and control module 33 information concerning the current flowing in and the voltage across the filament 8 immediately after the feeding phase thereof carried out by a pulsating current supplied by the module 31 feeding the filament 8.
An 8 bit microprocessor and four summing circuits are used for processing the signal Ia from the measurement stage 32. The signal Ia is simultaneously applied to the analog input of the 8 bit microprocessor and to the analog input of the four summing circuits.
Depending on the entering current level, a proportional output signal is generated by the four summing circuits and applied thereafter to four different analog inputs of the microprocessor in accordance with the following relationship:
Outi =K(Ia -500 i)
where 0≦i≦3 and K=5 V/60 nA
The voltage of the signals Out0 . . . Out3, will be proportional to the level of the current drawn by the ion pump and therefore to the helium concentration within the capillary membrane, and is shown in FIG. 7.
The level of the represented signals allows for defining nine evaluation bands or zones of the ion current level, each one excluding the others, shown in FIG. 7 with the references Z1 . . . Z9.
Such bands are discriminated into four groups by the 8 bit microprocessor according to the following criteria:
if the level of the output Out0 is lower or equal to zero, band Z1, then the microprocessor sets Ic =0;
if the level of the output Out3 is higher than 5 V, which means a current level Ia >210 nA, band Z9, then the microprocessor sets Ic =Ia ;
if both conditions 0 V<Outi <5 V and 0 V<Outi+1 <5 V with 0≦i≦2, bands Z3, or Z5 or Z7, then the current is calculated as the mean value of the current values in accordance with the following equation: ##EQU1## if 0.83 V<out1 <4.16 V, bands z2, Z4, Z6 and Z8, then the current is calculated in accordance with the equation I=(Out1 /K+50.i). Under these conditions the current signal I, is divided in the range 0-200 nA into four current levels further processed by the 8 bit microprocessor thereby achieving a resolution better than 0.25 nA when the current drawn by the ion pump is in the range from 0 to 200 nA, and a resolution of 10 nA over the whole working range which is typically from 0 to 2 μA.
In presence of helium the temperature of the capillary has to be reduced to prevent the saturation of the sampling chamber with a consequent response delay when passing from a high helium concentration zone to a zone devoid of helium.
To this aim there has been provided a module for evaluating the capillary temperature that uses the temperature information of the heating filament wound about it, calculated on the basis of the current and the voltage of the filament in a phase immediately subsequent to the phase of pulsating feeding. In other words a stage 31 for feeding pulses to the filament 8 through the connections 22 and 23, supplies a pulsating voltage that raises the temperature of filament 8 to a temperature tx. The immediately subsequent measurements of the voltage and the current of the filament provide an indication of its temperature in accordance with the following relationship:
tx =(1/Q).(Rt /Ro -1+to)
where Rt is the filament resistance at the temperature tx expressed as the ratio of the voltage to the current according to Ohm law; whereas Ro is the known filament resistance at the temperature to, and Q is the proportionality constant of the material used for making the filament.
The duration of the pulsating voltage applied to the filament 8 is changed as a function of the measured current Ic drawn by the ion pump, in accordance with an optimized criterion for keeping it lower or equal to a predetermined steady state value Ireg. In case the current drawn by the ion pump tends to increase due to an increase of the helium concentration and exceeds the predetermined threshold Ireg, or in case the change of such current exceeds the threshold Ider, then the duration of the voltage pulse applied to the filament is shortened allowing the capillary to cool, that is to become less permeable to helium and therefore to allow the capillary to be emptied by the pump and be brought back to levels of the drawn current that are equal or lower than those of the steady state Ireg.
A maximum temperature threshold Tmax is provided for in order not to exceed the critical heating levels when the helium concentration is quite low and the current drawn by the ion pump does not reach the steady state level Ireg.
The helium concentration is calculated according to the following relationship: ##EQU2## that takes into account the geometry of the capillary, the constant S, the volume and the pumping rate of the ion pump, the constant Γ which depends upon the volume of the capillary membrane and the pumping rate of the ion pump, the bottom current I0 and the quartz permeability to helium, i.e. the term ##EQU3##
In case the helium bottom concentration changes due to a change of the air conditions in the operating environment, the new bottom current level can be stored, and the unit will either be operated in a "fixed zero" manner or let it be automatically calculated operating in an "automatic zero" condition with an integration time of about 10 seconds.
With reference to FIG. 5, there are shown in the current Ia and the temperature T of the filament versus the helium concentration of the air to be sampled. For modest changes of the helium concentration, that is about 50 ppm, the filament temperature does not undergo changes since the slope of the ion current, and therefore the derivative thereof, is below the threshold for deenergizing the filament heating. For large changes, that is about 500 ppm, the filament temperature decreases since the ion current exceedes both thresholds, on the derivative and on the level Ireg, bringing again the ion current to steady state values.
For speeding up the depletion phase of the quartz capillary when this latter is saturated with helium, an additional control of the current drawn by the pump has been introduced allowing this current to reach a value of 1 μA before the filament temperature is raised again.
This way the depletion speed of the ion pump becomes ten times larger than that of the normal working conditions with a quicker removal of the accumulated helium.
To prevent the unit from being employed when its working would not be the optimum due to a clogging caused by dust or other external agents, there is provided a cycle for controlling the proper working of the inflow channel of the gas to be sampled, which is automatically actuated at each triggering of the sampling pump. This control cycle compares the power P0 drawn by the pump when the sampling pump is deenergized with the power P1 drawn when the pump has been triggered. When the two power values P0 and P1 are equal, or in case power P1 is lower than P0, a fault situation is shown on the display 35 and the operator is warned accordingly.
A module 33 for starting and checking the pump triggering is provided for ensuring a correct working of the pump even in conditions that are particularly unfavourable for the triggering thereof, typically when the pressure is below 1E-9 mbar.
With reference to FIG. 6 such triggering module comprises a phase I01 starting the pump at 6,000 V for about 10 seconds. During this phase I01 the heater of the capillary membrane is energized and the maximum threshold Ireg of the current drawn by the ion pump is maintained at 1 μA. In the second phase I02 of such cycle the pump working voltage is lowered to 3,000 V and consequently the current I' drawn by the ion pump is reduced. Then in a third phase I03 the pump working voltage is measured. Then phase I04 provides for a comparison phase in which the pump will surely be triggered if the measured current I' is larger than 5 nA which is the maximum dispersion current (equivalent to the current drawn by the ion pump when the inside pressure is zero) drawn by the ion pump at 3,000 V. In case such current I' is smaller than 5 nA, a further control will be executed by switching off the heater for about 4 seconds, phase I05, and measuring againg the current I" drawn by the ion pump, phase I06. In case after such comparison, phase I07, the current I" is smaller than the previous current I', the ion pump will be triggered, otherwise the triggering cycle will be activated again for a further attempt.
The affirmative outputs of phases I07 and I04 are followed by phase I08 that activates the working cycle of the unit.
With the above illustrated embodiment it was possible to detect helium concentrations in the air comprised between 1 ppm and 1E+6 ppm with a response time of about 2 seconds at a temperature of the capillary of about 550° and with a drawn power of about 10 W.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3803900 *||Jun 14, 1972||Apr 16, 1974||Commissariat Energie Atomique||Leak detection devices|
|US4111554 *||Feb 17, 1976||Sep 5, 1978||Compagnie Francaise De Raffinage||Process for the specific quantitative detection of sulfur compounds and apparatus for carrying out this process|
|US4492110 *||Jun 1, 1983||Jan 8, 1985||Martin Marietta Corporation||Ultra sensitive noble gas leak detector|
|US5019517 *||Apr 15, 1988||May 28, 1991||Coulson Dale M||System, detector and method for trace gases|
|US5134877 *||Feb 8, 1991||Aug 4, 1992||Alcatel Cit||Portable, counterflow helium leak detector for testing an enclosure having its own pumping equipment|
|EP0352371A2 *||Nov 11, 1988||Jan 31, 1990||VARIAN S.p.A.||Detector for helium leaks|
|IT1179600A *||Title not available|
|IT1224604A *||Title not available|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5661229 *||Jul 14, 1994||Aug 26, 1997||Leybold Aktiengesellschaft||Test gas detector, preferably for leak detectors, and process for operating a test gas detector of this kind|
|US5716011 *||Apr 5, 1995||Feb 10, 1998||L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude||Process for diffusing an odoriferous substance|
|US6945092 *||Jun 20, 2002||Sep 20, 2005||Inficon Gmbh||Method for operating a film leak indicator and a corresponding film leak indicator for carrying out said method|
|US7290439 *||Jun 9, 2004||Nov 6, 2007||Varian, Inc.||Methods and apparatus for leak detection by the accumulation method|
|US7320243 *||Jun 9, 2004||Jan 22, 2008||Varian, Inc.||Methods and apparatus for detection of large leaks in sealed articles|
|US7497110||Feb 28, 2007||Mar 3, 2009||Varian, Inc.||Methods and apparatus for test gas leak detection|
|US7977107||Oct 1, 2010||Jul 12, 2011||Labone, Inc.||Oral detection test for cannabinoid use|
|US8453493||Nov 2, 2010||Jun 4, 2013||Agilent Technologies, Inc.||Trace gas sensing apparatus and methods for leak detection|
|US8629410 *||Jun 3, 2010||Jan 14, 2014||Hitachi High-Technologies Corporation||Charged particle radiation device|
|US20030233866 *||Jun 20, 2002||Dec 25, 2003||Inficon Gmbh||Method for operating a film leak indicator and a corresponding film leak indicator for carrying out said method|
|US20050223779 *||Jun 9, 2004||Oct 13, 2005||Charles Perkins||Methods and apparatus for leak detection by the accumulation method|
|US20060094123 *||Nov 3, 2004||May 4, 2006||David Day||Oral detection test for cannabinoid use|
|US20060156795 *||Jun 9, 2004||Jul 20, 2006||Charles Perkins||Methods and apparatus for detection of large leaks in sealed articles|
|US20080202210 *||Feb 28, 2007||Aug 28, 2008||Varian, Inc.||Test gas leak detection using a composite membrane|
|US20080202212 *||Feb 28, 2007||Aug 28, 2008||Varian, Inc.||Methods and apparatus for test gas leak detection|
|US20090149546 *||Jan 9, 2009||Jun 11, 2009||Chin-Ming Chang||Enhanced Bimatoprost Ophthalmic Solution|
|US20090159792 *||Nov 13, 2008||Jun 25, 2009||Labone, Inc.||Oral Detection Test for Cannabinoid Use|
|US20120091362 *||Jun 3, 2010||Apr 19, 2012||Hitachi High-Technologies Corporation||Charged particle radiation device|
|CN1720432B||Jun 9, 2004||Sep 29, 2010||瓦里安有限公司||Methods and apparatus for detection of large leaks in sealed articles|
|EP1555520A1 *||Jan 13, 2004||Jul 20, 2005||VARIAN S.p.A.||Leak detector|
|EP2042849A1||Sep 26, 2008||Apr 1, 2009||Alcatel Lucent||Device and method for detecting high-pressure leaks using tracer gas in a part to be tested|
|WO2005001410A1||Jun 9, 2004||Jan 6, 2005||Varian, Inc.||Methods and apparatus for leak detection by the accumulation method|
|U.S. Classification||73/40.7, 73/23.2|
|Cooperative Classification||G01M3/202, G01M3/20|
|European Classification||G01M3/20, G01M3/20B|
|Aug 21, 1992||AS||Assignment|
Owner name: VARIAN S.P.A., ITALY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:DE SIMON, MAURO;REEL/FRAME:006210/0379
Effective date: 19920612
|Dec 15, 1997||FPAY||Fee payment|
Year of fee payment: 4
|Jan 4, 2002||FPAY||Fee payment|
Year of fee payment: 8
|Jan 30, 2002||REMI||Maintenance fee reminder mailed|
|Jan 5, 2006||FPAY||Fee payment|
Year of fee payment: 12
|May 19, 2011||AS||Assignment|
Owner name: AGILENT TECHNOLOGIES ITALIA S.P.A., ITALY
Free format text: MERGER;ASSIGNOR:VARIAN, S.P.A.;REEL/FRAME:026304/0761
Effective date: 20101101